Lookup field compared to FlowField

Hello I want to add a field lookup to my project. I which to add some date-fields to the salesorderline coming for the linked purchaseorderline for drop-shipments. If I add a lookup-field to the salesorderline tableI I get a compilation error: Deployment failed. Errors: App ID : cac5868c-9eb1-4962-8cb8-6a80f866c440 Message : { Extension compilation failed
TableExtensions/Sales_Line_TableExt.al(49,46): error AL0193: Argument 2: cannot convert from 'Date' to the type of Argument 1 'Integer' } Seems like there is a wrong type for the Lookup-field. Not something I seem to control... In order to work around this problem I have tried looking up non-datefields. Then the compilation passes, but no data is transferred to the field. It is empty even if the correcsponding purchaseorderline contains data. In order to find another way through the problem, I have changed the field to a Flowfield. Then everything works! The correct data is fetched from the purchaseorderline. Also for the datefield. But I do not need to link-functionality of the Flow-field, so I would still like to make the Lookup-field work. Any ideas to how I can make this work with the Lookup-field? BR. Henrik Madsen